📚 Year 12 CAIE Biology: Core Knowledge Review | 12年级 CAIE 生物：核心知识点梳理
This revision guide covers the essential topics for Year 12 CAIE AS Biology, including cell structure, biological molecules, enzymes, membrane transport, cell division, nucleic acids, plant and animal transport, gas exchange, and immunity. Mastering these core concepts is vital for success in the exams and building a strong foundation for A2.
本复习指南涵盖了 12 年级 CAIE AS 生物的核心主题，包括细胞结构、生物分子、酶、膜运输、细胞分裂、核酸、植物与动物运输、气体交换和免疫。掌握这些核心概念对考试成功和为进一步学习 A2 打下坚实基础至关重要。
1. Cell Structure | 细胞结构
Eukaryotic cells possess membrane-bound organelles, including a true nucleus that stores genetic material (DNA) as chromatin.
真核细胞具有膜包被的细胞器，包括储存遗传物质 (DNA) 的真核，遗传物质以染色质形式存在。
The cell surface membrane is a phospholipid bilayer with embedded proteins; it controls the passage of substances in and out of the cell.
细胞表面膜是嵌入蛋白质的磷脂双分子层；它控制物质进出细胞。
Mitochondria have a double membrane; the inner membrane is folded into cristae, providing a large surface area for aerobic respiration and ATP production.
线粒体有双层膜；内膜折叠成嵴，为有氧呼吸和 ATP 生成提供大表面积。
Ribosomes (80S in eukaryotes, 70S in prokaryotes and organelles) are the sites of protein synthesis, composed of rRNA and proteins.
核糖体（真核生物中为 80S，原核生物和细胞器中为 70S）是蛋白质合成的场所，由 rRNA 和蛋白质组成。
In plant cells, chloroplasts carry out photosynthesis, a large permanent vacuole maintains turgor pressure, and the cellulose cell wall provides structural support.
在植物细胞中，叶绿体进行光合作用，一个大液泡维持膨压，纤维素细胞壁提供结构支撑。
Prokaryotic cells lack a nucleus and membrane-bound organelles; they have a cell wall, circular DNA, and smaller 70S ribosomes.
原核细胞没有细胞核和膜包被的细胞器；它们具有细胞壁、环状 DNA 和较小的 70S 核糖体。
2. Biological Molecules | 生物分子
Carbohydrates are composed of carbon, hydrogen and oxygen, with the general formula Cx(H₂O)y. Monosaccharides such as glucose are reducing sugars.
碳水化合物由碳、氢和氧组成，通式为 Cx(H₂O)y。葡萄糖等单糖是还原糖。
Disaccharides (maltose, sucrose, lactose) are formed by a condensation reaction between two monosaccharides, linked by a glycosidic bond.
二糖（麦芽糖、蔗糖、乳糖）由两个单糖通过糖苷键连接，经缩合反应形成。
Polysaccharides serve as energy stores (starch in plants, glycogen in animals) or structural components (cellulose in cell walls). Cellulose has β-1,4 glycosidic bonds that form straight chains, strengthened by hydrogen bonds.
多糖作为能量储存（植物中的淀粉、动物中的糖原）或结构成分（细胞壁中的纤维素）。纤维素具有 β-1,4 糖苷键，形成直链，由氢键加固。
Lipids are non-polar macromolecules; triglycerides consist of one glycerol molecule esterified with three fatty acids. Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails, forming the basis of membranes.
脂质是非极性大分子；甘油三酯由一个甘油分子与三个脂肪酸酯化形成。磷脂具有亲水磷酸头端和两个疏水脂肪酸尾端，构成膜的基础。
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the sequence of amino acids; secondary structure includes α-helices and β-pleated sheets held by hydrogen bonds; tertiary structure is the overall 3D folding, stabilised by ionic bonds, disulfide bridges, hydrophobic interactions and hydrogen bonds.
蛋白质是由氨基酸通过肽键连接而成的多聚体。一级结构是氨基酸序列；二级结构包括 α-螺旋和 β-折叠，由氢键维持；三级结构是整体的三维折叠，由离子键、二硫键、疏水作用和氢键稳定。
Water is a dipolar molecule forming hydrogen bonds, which leads to its properties of cohesion, high specific heat capacity, high latent heat of vaporisation, and excellent solvent ability for polar substances.
水是偶极分子，能形成氢键，这使其具有内聚力、高比热容、高蒸发潜热和作为极性物质优良溶剂的能力。
3. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts by lowering the activation energy of reactions, without being consumed.
酶是球蛋白，作为生物催化剂，通过降低反应的活化能来加速反应，自身不被消耗。
The specificity of an enzyme is explained by the lock-and-key model and the induced-fit model, where the active site is complementary to the substrate and undergoes a conformational change upon binding.
酶的特异性可由锁钥模型和诱导契合模型解释，活性位点与底物互补，并在结合时发生构象变化。
Enzyme activity is affected by temperature: as temperature rises, kinetic energy increases, raising the rate up to an optimum; beyond this, denaturation occurs as hydrogen bonds break, altering the active site shape permanently.
酶活性受温度影响：温度升高，动能增加，速率提升至最适温度；超过之后，氢键断裂导致变性，活性位点形状永久改变。
pH affects the charge of amino acid residues at the active site, disrupting ionic and hydrogen bonds. Each enzyme has an optimum pH; extreme pH leads to denaturation.
pH 影响活性位点氨基酸残基的电荷，打乱离子键和氢键。每种酶有其最适 pH；极端 pH 会导致变性。
Competitive inhibitors resemble the substrate and bind reversibly to the active site, so increasing substrate concentration can overcome inhibition. Non-competitive inhibitors bind to an allosteric site, changing the enzyme's shape and reducing Vmax without affecting Km.
竞争性抑制剂与底物相似，可逆地结合活性位点，因此增加底物浓度可以克服抑制。非竞争性抑制剂结合别构位点，改变酶的形状，降低 Vmax 但不影响 Km。
At high substrate concentration, the rate reaches Vmax because all active sites are occupied, forming a plateau on the rate-substrate graph.
在高底物浓度下，速率达到 Vmax，因为所有活性位点都被占据，速率-底物图上出现平台。
4. Cell Membranes and Transport | 细胞膜与物质运输
The fluid mosaic model describes the membrane as a dynamic phospholipid bilayer with proteins floating within, held together by hydrophobic interactions.
流动镶嵌模型将膜描述为动态的磷脂双分子层，蛋白质漂浮其中，通过疏水作用聚合在一起。
Integral proteins span the bilayer and can act as channels or carriers; peripheral proteins are attached to the surface and function in signaling or structural support. Cholesterol in animal membranes regulates fluidity.
整合蛋白横跨双分子层，可充当通道或载体；外周蛋白附着在表面，参与信号转导或结构支持。动物膜中的胆固醇调节流动性。
Simple diffusion is the passive movement of small, non-polar molecules (e.g. O₂, CO₂) down a concentration gradient through the phospholipid bilayer.
简单扩散是小而非极性分子（如 O₂、CO₂）顺浓度梯度穿过磷脂双分子层的被动运动。
Facilitated diffusion uses channel proteins (for ions) and carrier proteins (for larger polar molecules such as glucose) to move substances down the concentration gradient without ATP.
易化扩散利用通道蛋白（用于离子）和载体蛋白（用于葡萄糖等较大极性分子）顺浓度梯度运输物质，不需要 ATP。
Osmosis is the net movement of water molecules from a region of higher water potential (less negative) to a region of lower water potential (more negative) through a partially permeable membrane.
渗透是水分子通过部分透性膜从水势较高（负值较小）的区域向水势较低（负值较大）的区域净移动。
Active transport uses carrier proteins (pumps) to move substances against the concentration gradient, coupled with the hydrolysis of ATP. Examples include the Na⁺/K⁺ pump.
主动运输利用载体蛋白（泵）逆浓度梯度移动物质，与 ATP 水解偶联。例如 Na⁺/K⁺ 泵。
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